Filter comprising membranes made of hollow fibers

ABSTRACT

The invention relates to a filter comprising membranes made of hollow fibers (21) in which the hollow fibers ( 21 ) are arranged as a bundle ( 19 ) in a tubular housing ( 3 ). The housing ( 3 ) comprises an end cap ( 5 ) on each of its ends, whereby the hollow fiber bundle ( 19 ) is placed between the ends of the housing ( 3 ). The ends of the hollow fiber bundle ( 19 ) each comprise a support ring ( 40 ) that surrounds the same and are cast inside said support ring ( 40 ). The support ring ( 40 ) comprises axially protruding catches ( 42 ) and is displaceably mounted in the housing ( 3 ) in order to compensate for, in particular, axial contractions of the hollow fiber bundle ( 19 ) occurring during heat sterilization.

[0001] The present invention relates to a filter comprising membranesmade from hollow fibres, in which the hollow fibres are provided as abundle arranged in a tubular housing. The housing is provided at eachend with an end-cap, wherein the hollow-fibre bundle is arranged betweenthe ends of the housing, a support-ring for each end of the hollow fibrebundle is arranged around each respective end of the hollow-fibrebundle, which ends are cast within a potting compound, and the ends ofthe hollow fibres are open.

TECHNICAL BACKGROUND

[0002] Filters having hollow-fibre membranes are used i.a. in the areaof dialysis for a wide variety of purposes. Such filters are used, forexample, in haemodialysis, in which blood is directed into and throughthe inside of the semi-permeable walls of the hollow fibres whiledialysis fluid is directed around the outside of the hollow fibres.Various convection and diffusion processes thereby take place throughthe walls of the hollow fibres, which processes serve to purify theblood and to remove excess fluid. Additionally, due to this, theelectrolyte concentration in the blood can be conditioned, and bufferssuch as bicarbonate or acetate can be added to the blood.

[0003] Filters of this type are also employed in so-calledhaemofiltration, in which a substitution fluid is added to the blood.According to this process, the blood is directed through the inside ofthe hollow fibres, although in this case no dialysis fluid is passedaround the outside of the fibres. Here, in the filter, excess fluids, inparticular water as well as waste products, are removed from the bloodonly by means of a pressure difference across the membrane, i.e. thesemi-permeable walls of the hollow fibres. The substitution fluid can beadded either before or after the filter.

[0004] The above-mentioned filters can equally be used as so-calledultrafilters for the production of the substitution fluid. In this case,dialysis fluid can for example be directed through the inside of thehollow fibres and can, by means of a pressure difference, be filteredthrough the membrane or semi-permeable walls, whereby the dialysis fluidcan be sterile-filtered as a result of the removal of endotoxins,bacteria and other contaminants.

[0005] Further uses for the filters mentioned includehaemodiafiltration; a combination of haemodialysis and haemofiltration,as well as plasmapheresis, in which the aqueous blood-plasma is filteredout of the blood and returned to the blood again after treatment. Suchfilters are also used in reverse osmosis.

[0006] The aforementioned filters are usually so constructed that thehollow-fibres are arranged as a loose bundle collected together within atubular housing. The housing is provided at each end with an end-cap,whereby the hollow-fibre bundle is arranged between the ends of thehousing so that the end-caps cover the ends of the hollow-fibre bundle.A support ring is provided around each end of the hollow-fibre bundle,while the ends of the hollow fibres are embedded within a pottingcompound at the ends of the housing.

[0007] The hollow fibres collected together in the hollow fibre bundlehave ends which open into a hollow space located between the end cap andthe end of the hollow-fibre bundle. It is therefore possible, with theappropriate arrangement of inlets and outlets, to provide, in a knownmanner, various forms of filter, such as the previously mentionedhaemodialysis filters, haemofilters, haemodiafilters, ultrafilters etc..

[0008] Examples of the previously mentioned filters are disclosed inEP-0 305 687, EP-0 355 325 and EP-0 525 317.

[0009] Essentially, all the previously mentioned filters have certainfeatures in common, namely that a first fluid is directed into andthrough the inside of the semi-permeable hollow fibres while a secondfluid is present on the outside of the hollow fibres. This second fluidcan either flow through the housing, past and around the hollow fibres,via appropriately located inlet and outlet means; or it can for examplebe removed from the first fluid and directed out of the housing via asuitable outlet, for example by means of a pressure differential acrossthe hollow-fibre membrane.

[0010] A disadvantage of the previously mentioned filters can be seen inthat during the usual heat-sterilisation process, for example usingsteam, shrinkage of the hollow fibres occurs, in particular withsynthetic hollow fibres. These mainly axial shrinkages of the hollowfibres can lead to damage or in worse cases to leakage, especially whenthe extent of the shrinkage cannot be compensated for by the elasticityof the hollow fibres.

[0011] It is clear, especially during the above-mentioned uses of thesefilters, that any leakage of the hollow fibre membrane should be avoidedin all circumstances. A leakage in just a single fibre could lead to aserious risk for a patient.

Description of the Invention

[0012] Against this background, the problem which the present inventionseeks to solve is that of providing a filter having hollow-fibremembranes in which the hollow fibres are arranged as a bundle within atubular housing and in which the housing is provided with an end-cap ateach end thereof, wherein the hollow-fibre bundle is arranged betweenthe ends of the housing, and wherein a support ring is arranged aroundeach end of the hollow-fibre bundle, the ends of the hollow-fibres beingembedded within a potting compound and wherein the ends of the hollowfibres are open, and furthermore, wherein the hollow fibres are notsusceptible to damage resulting from axial shrinkage.

[0013] This problem is solved by a filter of the aforementioned type,wherein the end of the hollow-fibre bundle is embedded substantiallyonly within the support ring by means of the potting compound.

[0014] A filter is thereby provided, which is substantially invulnerableto a heat or steam sterilization process. The term invulnerable as usedherein is to be understood as meaning that the unavoidable shrinkagewhich occurs, in the present case in particular the axial shrinkage ofthe hollow fibres, does not lead to damage of the hollow fibres.

[0015] This arises from the fact that the hollow-fibre bundle isattached only to the support ring and not to the housing, thus allowinga limited degree of movement of the hollow-fibre bundle together withthe support ring within the housing. In this way, the shrinkage arisingfrom heat or steam sterilization can be compensated, since thehollow-fibre bundle, or alternatively, the individual hollow fibres, isthereby capable of following the shrinkage and yielding in response toit. Leakages and damage to the hollow fibres can thus be effectivelyavoided.

[0016] When, in accordance with a preferred embodiment, the support ringfurther comprises axially projecting lugs, which lugs are preferablyarranged on the side of the support ring facing the centre of thehousing, whereby the lugs are preferably formed to be flexible, thesupport ring is especially axially movable.

[0017] The term flexible is here to be understood as meaning compliantin the sense that the lugs are formed so as to be compressible orfoldable. When for example a corresponding compressive force is appliedto the support ring in an axial direction, the lugs will be compressedor folded against a correspondingly formed shoulder on the housing andthe support ring pushed axially in the direction of the compressiveforce until it again rests, with other parts or regions, against theshoulder on the housing.

[0018] This provides the added significant advantage that axialshrinkages of the hollow-fibre bundle of the kind occurring, forexample, during heat-sterilisation of in particular synthetic hollowfibres, can be compensated. To this end, during fabrication of thefilter, the entire hollow-fibre bundle is axially compressed such thatthe embedded ends of the hollow-fibre bundle are shifted by a fewmillimeters towards each other. This has the effect that the individualhollow fibres in the hollow-fibre bundle and within the housing arerelatively slack or loose, similar to a loose bundle of strings. Thehollow fibres, embedded at either end within the potting compound, canthus undergo some axial contraction and thereby compensate for axialshrinkages arising for example from heat sterilization, without becomingdamaged or being torn apart. For example, through an appropriateconfiguration of the flexible lugs, and by compressing each end of thehollow-fibre bundle by just two millimeters in a direction towards thecentre of the housing, a compensation capability for the hollow fibresof up to four millimetres can be provided.

[0019] The axially protruding, flexible lugs may of course bedifferently dimensioned, and they may for example be longer, so that agreater compression of the hollow-fibre bundle is possible byapplication of a compressive force on the support ring. The axiallyprotruding lugs are thereby bent or compressed, thus allowing a movementof the support ring and with it of the embedded end of the hollow-fibrebundle in an axial direction, i.e. relative to the filter housing.

[0020] Whilst it may seem redundant, it is nevertheless pointed out atthis stage, that a compression of the hollow-fibre bundle is onlypossible when its ends are embedded within the respective support ring.Accordingly, the potting compound must lie only within the support ring,in order to avoid a connection between the support ring and the housing.The potting compound may be comprised of any suitable material such as,for example, polyurethane (PUR).

[0021] In addition, the axially protruding, flexible lugs may beaccommodated on the housing in an appropriate manner instead of on thesupport ring. The axial movability of the support ring is thereby alsoenabled, allowing axial shrinkage of the hollow fibres and thereby alsoof the hollow-fibre bundle to be compensated.

[0022] For the compensation of axial shrinkage, the hollow fibre bundlemay be axially compressed during the fabrication process, as describedabove. This allows, so to speak, a compensation of axial shrinkage inadvance, before its occurrence. Alternatively, the hollow fibre bundleis not compressed in advance, and instead the compensation of axialshrinkage of the hollow fibres may take place simultaneously with itsoccurrence. Accordingly, the flexibly formed lugs allow the contractinghollow fibres within the housing to thereby draw the axially movablesupport rings in a direction towards the centre of the housing.

[0023] In order to seal the filter, or the housing, the end-cap issealingly connected to the housing. The embodiment to be chosen for thisfeature depends upon the constructive arrangement of the filter. Thesealing connection of the parts with one another may be achieved by theuse of adhesive means, by welding, or by means of a seal between therespective parts. For example, elastic sealing rings or the like may beused for this.

[0024] The sealing connection forming the seal between the first and thesecond fluid containing areas may also be achieved by use of adhesive,by welding or by means of appropriate seals such as, for example,O-rings.

[0025] It should be noted at this point, that the previously mentionedaxial movability as well as a certain radial movability of the supportring, i.e. its movability relative to the housing, is only possible whenthe support ring is not fixed to either the end-cap or to the housing orboth, whether by adhesive or by welding means. Only then does a certainrelative movability of the support ring and thereby of the hollow-fibrebundle remain within the finished filter.

[0026] Finally, according to a preferred embodiment, the filter isadvantageously provided with an inlet and an outlet for a first fluid,as well as at least one outlet for a second fluid. Preferably, the inletfor the first fluid is arranged on one end-cap, while the outlet for thefirst fluid is provided on the other end-cap, so that the first fluidmay be readily directed into the housing, through the inside of thehollow-fibre bundle and out of the housing on the other side. The outletfor the second fluid can be accommodated on an end-cap or on thehousing, depending upon the intended use of the filer.

[0027] According to another preferred embodiment, the filter is providedwith an inlet for the second fluid, which is preferably accommodated onan end-cap or on the housing.

DESCRIPTION OF THE DRAWINGS

[0028] The invention will now be described in more detail in the contextof a preferred embodiment with reference to the attached drawings. Theseshow:

[0029]FIG. 1-a partial-section of a filter according to the state of theart;

[0030]FIG. 1A-an enlarged partial view of FIG. 1, showing a longitudinalsection of the end of the hollow-fibre bundle with the support ring;

[0031]FIG. 2-a longitudinal section through one half of a filteraccording to the present invention with a compressed hollow-fibrebundle;

[0032]FIG. 3-an enlarged partial view of FIG. 2, showing the end of thehollow-fibre bundle with the support ring;

[0033]FIG. 4-a longitudinal section though one half of a filteraccording to the invention, prior to the application of the pottingcompound and prior to compression;

[0034]FIG. 5-an enlarged partial view of FIG. 4;

[0035]FIG. 6-a longitudinal section through one half of a filteraccording to the invention after the application of the potting compoundand after the axial compression;

[0036]FIG. 7-an enlarged partial view of FIG. 4.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0037]FIG. 1 depicts a partial longitudinal view of a filter 1 accordingto the state of the art. The filter 1 has a tubular filter housing 3,which has an end-cap 5 attached at each end. Each end-cap 5 has an inlet7 or outlet 9 for a first fluid, each of which is provided with aninternal screw-thread 11. The end-caps 5 are furthermore provided withan inlet 13 or outlet 15 for a second fluid, each of which is providedwith an external screw-thread 17. Within the tubular housing 3, ahollow-fibre bundle 19 is arranged, which extends between the ends ofthe housing 3. The ends of the hollow-fibre bundle 19 are surrounded bya support ring 23 and are embedded into the ends of the housing 3 bymeans of a potting compound 70.

[0038] The filter 1 functions as follows: connection tubes for a firstfluid are connected to the inlet 7 and outlet 9 by means of the internalscrew-thread 11. Similarly, connection tubes for a second fluid areconnected to the inlet 13 and to the outlet 15 by means of the externalscrew-thread 17 provided. A first fluid is then directed through theinlet 7 towards the end of the hollow-fibre bundle 19. The ends of thehollow fibres 21, which make up the hollow-fibre bundle 19, are open andare comprised within the ends of the hollow-fibre bundle 19, so that thefirst fluid can be directed inside the hollow fibres 21 and through tothe other side of the filter 1. There, the first fluid emerges from theend of the hollow-fibre bundle 19 and is conducted away through theoutlet 9.

[0039] A second fluid is conducted into the housing 3 via the inlet 13,where it then flows along the outside of the hollow fibres 21 of thehollow-fibre bundle 19 to the other end of the housing 3, from where itis conducted away through the outlet 15.

[0040] The first fluid and the second fluid are conducted past oneanother in opposite directions and on different sides of thehollow-fibre membrane 21, during which various known convection anddiffusion processes take place through the walls of the hollow fibres.

[0041]FIG. 1A depicts an enlarged partial view of FIG. 1 showing the endof the hollow-fibre bundle 19. The hollow-fibre bundle 19 is surroundedat its end region by a support ring 23, which support ring 23 has afirst portion 25 and a second portion 29. The first portion 25 isprovided with a number of radial flanges 27 which connect the firstportion 25 to the housing 3. The flanges 27 are configured such thatthey support the support ring 23 both axially and radially. Theperipheral first portion 25 is additionally provided with further radialflanges 31 by means of which it is connected with the second peripheralportion 29. The second portion 29 surrounds the end portion of thehollow-fibre bundle 19. This end-portion of the hollow-fibre bundle 19,along with the support ring 23, is potted within the end of the housing3 by means of a potting compound 70. The second portion 29 of thesupport ring 23 is thereby completely enclosed within the pottingcompound 70.

[0042] The end-cap 5 is placed on the housing 3 and is sealinglyattached to the housing 3 by an adhesive 74. The end-cap 5 is also fixedto the potting compound 70 by the same adhesive 74 and is in radialcontact with the outside of the first portion 25 of the support ring 23.

[0043] A ring 72 of potting compound 70, is disposed between theperiphery of the hollow-fibre bundle 19 and the inside of the end-cap 5and has a broad width. This arrangement prevents penetration of adhesive74 into the hollow fibres 21, the open ends of which are disposed in theend of the hollow-fibre bundle.

[0044]FIG. 2 shows a longitudinal section of a filter 100 according tothe invention, in which for the sake of simplicity only one half of thefilter is shown and in which equivalent parts have been given the samereference numeral. The filter 100 has a tubular housing 3 and an end cap5, one of which is shown, attached to each end of the housing 3. Theend-cap 5 has an outlet 7 which comprises an internal screw-thread 11.The housing 3 further comprises an outlet 15 for a second fluid, thesaid outlet 15 having an external screw-thread 17. A hollow-fibre bundle19 comprised of hollow fibres 21 is arranged within the housing 3, thehollow-fibre bundle 19 having been compressed. The end of thehollow-fibre bundle 19 is potted into a support ring 40 by means of apotting compound 70.

[0045] The support ring 40 is provided at one end with a plurality oflugs 42, which will be described more fully in the following descriptionof the support ring 40, along with the rim 44, the flanges 46 and thesteps 48 and 50.

[0046] It should be noted at this point, that an alternative arrangementof the inlets and outlets could also be provided, as is known to oneskilled in the art. For example, the outlet 15 could equally be arrangedon the end-cap 5.

[0047]FIG. 3 shows an enlarged partial view of FIG. 2, showing the endof the hollow-fibre bundle 19 potted into the support ring 40. Alsohere, equivalent parts are given the same reference numeral.

[0048] The support ring 40 is provided, at its end facing the end-cap 5,with an inwardly protruding shoulder 44 with flanges 46. The rim 44 andthe flanges 46 attached to it create a fitted connection between thesupport ring 40 and the potting compound 70, in addition to the adhesiveconnection between the potting compound 70 and the support ring 40. Onits outside, the support ring 40 is provided with two steps 48 and 50,which rest upon correspondingly shaped shoulders 52 and 54 on thehousing 3. At its lower end, the support ring has a plurality offlexible lugs 42, one of which is illustrated here. The flexible lug 42is bent and extends into a corresponding recess 58 in the housing 3.

[0049] According to the present embodiment, the end-cap 5 is sealinglyconnected to the housing 3 at a connection portion 64, as shown here bymeans of welding, for example using ultrasound. A further possibility,from among several others, involves bonding, using suitable adhesivemeans known to the skilled person. The end-cap 5 is provided at itsperiphery with a recess 62, in which a sealing ring 60 is accommodated.This sealing ring 60 delimits the peripheral region of free space formedbetween the end-cap 5 and the end of the hollow-fibre bundle 19, suchthat only a narrow ring 72 of the potting compound is present in theaforementioned free space. This improves the flow characteristics of thefirst fluid which is conducted into the hollow space via the inlet 7 ofthe end-cap 5, and from there passes into the open ended hollow fibres21, through which it flows to the opposite end of the filter housing 3.The improved flow characteristics create i.a. a flushing of the firstfluid through the peripheral region of the hollow space, i.e. the spaceabove the ring 72 of potting compound, so that a build-up of deposits isprevented. When the first fluid is comprised of blood for example, as isforeseen in the embodiments mentioned in detail above, this prevents theblood from being stationary and thereby from clotting. This therebygreatly reduces the risk of blood clots and thus renders theabove-mentioned examples of use or treatments considerably safer for thepatient.

[0050] In addition, the sealing ring 60 seals the region of the filterthrough which the first fluid flows from the region through which thesecond fluid flows.

[0051] The filter 100 shown in FIG. 3 is a finished filter, i.e. readyfor use. The hollow-fibre bundle 19 of the filter has been axiallycompressed, as can be readily seen from the bent flexible lug 42, whichhas been forced into the recess 58 of the housing 3. The function of theflexible lug 42, as well as that of the compression operation of thehollow-fibre bundle 19, will now be described in detail with referenceto FIGS. 4-8.

[0052]FIG. 4 shows a longitudinal section of an end of the filter 100prior to the application of the potting compound and prior to the axialcompression of the filter bundle 19. Here also, equivalent parts aregiven the same reference numeral.

[0053] The hollow-fibre bundle 19, placed within the filter housing 3,is held in place vis-{fraction (a)}-vis a mould ring 80. The mould ring80 is attached to the housing 3 at one end, and at its other end, bearsa moulding cover 82. The support ring 40 rests with its flexible lugs 42located upon a shoulder 56 on the housing. The dotted line 90 indicatesthe line along which the hollow-fibre bundle 19 is to be cut followingthe potting operation.

[0054] For the sake of a better understanding, the description will nowbe continued with reference to FIG. 5, in which an enlarged partial viewof FIG. 4 is depicted.

[0055] As can be clearly seen from FIG. 5, the mould ring 80 hasfastening means 84 at its end nearest the housing 3, which means 84engage with a correspondingly shaped projection on the housing 3 therebysecuring the mould ring 80 to the housing 3, together with theprojection 86, and the support ring 40, as will be explained in detail.Furthermore, as can readily be seen, the mould ring 80 has fasteningmeans 88 at its other end which cooperate with a correspondingly shapedportion of the moulding cover 82 to fix the moulding cover onto themould ring.

[0056] As is illustrated here, the flexible lug 42 of the support ring40 is not deformed prior to the axial compression and pottingoperations, and is seated on a shoulder 56 on the housing. The freespace between the step 48 of the support ring 40 and the shoulder 52 ofthe housing 3 is easily recognizable, as is the free space between thestep 50 of the support ring 40 and the shoulder 54 of the housing 3.

[0057] The above-mentioned protrusion 86 of the mould ring 80 rests uponthe step 48 of the support ring 40. The support ring 40, or its positionwithin the housing 3, is firstly thereby fixed. Secondly, the mould ring80, or its position in the housing 3, is consequently also fixed. Thestep 48 of the support ring 40 limits the movement of the protrusion 86and thereby also of the mould ring 80 in the direction towards thehousing 3, i.e. it limits the downward movement (FIG. 5), while thefastening means 84 of the mould ring 80 limit movement of the mould ring80 in a direction away from the housing 3, i.e. an upward movement (FIG.5). At the same time, the protrusion 86 of the mould ring 80 limits themovement of the support ring 40 away from the housing 3, while theflexible lug 42 which abuts the shoulder 56 on the housing 3, limits themovement of the support ring 40 towards the interior of the housing 3.

[0058] In the condition illustrated in FIG. 5, the filter 100 is readyfor the introduction of the potting compound for potting the end of thehollow-fibre bundle 19, or the hollow fibres 21 arranged therein. Forthis purpose, the potting compound is usually introduced through theoutlet 15 of the housing 3, and is then pushed into the mould ring 80and moulding cover 82 by centrifuge means, i.e. by rotation of thefilter 100, such that the hollow fibres 21 are cast together in order toseal the hollow-fibre bundle 19 at its ends.

[0059]FIG. 6 depicts a longitudinal section view of an end of the filter100 after the potting of the ends of the hollow fibres 21 with thepotting compound 70 as well as after the axial compression of the entirehollow-fibre bundle 19. Here again, equivalent parts are given the samereference numeral.

[0060] From FIG. 6, it can easily be seen that the potting compound 70casts the ends of the hollow fibres 21 together, so that a solid,cohesive end of the hollow-fibre bundle 19 is created. The pottingcompound 70 is distributed in the manner shown by virtue of thecentrifugal force, while the support ring 40 together with the mouldring 80 and moulding cover 82, define a mould for the potting compound.The potting compound 70 is thereby prevented from coming into contactwith, and adhering to, the housing 3. The relative movability betweenthe support ring 40 and the housing 3, necessary for the axialcompression of the hollow-fibre bundle 19, is thereby maintained, as isshown in FIG. 6. The compression operation causes the flexible lugs 42to bend and to be pushed outwards, such that they are slid into therecess 58 in the housing 3, thereby having enabled an axial movement ofthe support ring 40 along with the end of the hollow-fibre bundle 19,which end is potted into the support ring.

[0061] This can be more clearly seen from FIG. 7, which depicts anenlarged partial view of FIG. 6. Here also, equivalent parts are giventhe same reference numeral.

[0062] The end of the hollow-fibre bundle 19 is pushed towards thecenter of the housing 3 by virtue of the compression operation. As aresult of this, the flexible lugs, which abut the shoulder 56 of thehousing 3, are bent and forced into the recess 58 of the housing 3. Thehollow-fibre bundle 19 is shifted until such a time as the steps 48 and50 abut the corresponding shoulders 52 and 54 of the housing 3, as shownin FIG. 7. The configuration of the shoulders 52 and 54 on the housing 3thus determines the maximum axial compressibility of the hollow-fibrebundle 19. It is therefore necessary to arrange the shoulders 52 and 54in a configuration corresponding to the desired axial compression of thehollow-fibre bundle 19, while taking account of the material from whichthe hollow fibres 21 are comprised.

[0063] The axial compression of the hollow-fibre bundle 19 is carriedout by means of a compression force applied to the moulding cover 82and/or to the mould ring 80. The hollow-fibre bundle 19 is therebylongitudinally compressed, the flexible lugs 42 are bent and forced intothe recess 58, and the end of the hollow-fibre bundle 19 is partiallypushed into the housing 3. Since this is carried out simultaneously onboth ends of the housing 3, the hollow fibres 21 are thus relaxed by afew millimeters and thereby lie somewhat loose within the hollow-fibrebundle 19 and the housing 3. This enables them to readily compensateshrinkage of a few millimeters without breaking or otherwise beingdamaged.

[0064] As explained above at length, the relative movability between thesupport ring 40 or the hollow-fibre bundle 19 and the housing 3, isenabled by virtue of the potting compound 70 being containedsubstantially only within the support ring 40. This relative movabilityof the support ring 40 enables the compression of the hollow-fibrebundle 19, which later allows a compensation of longitudinal shrinkageof the hollow fibres 21. These shrinkages of the hollow fibres 21 are aconsequence of the final heat-sterilisation of the finished filter 100,and occur mainly in synthetic fibres.

1. Filter comprising membranes made from hollow fibres (21), in whichthe hollow fibres (21) are arranged in a bundle (19) within a tubularhousing (3), the housing (3) being provided at each end with an end-cap(5), wherein the hollow-fibre bundle (19) is arranged between the endsof the housing (3), and wherein each of the ends of the hollow-fibrebundle (19) is surrounded by a respective support ring (40), the ends ofthe hollow-fibre bundle (19) being cast by means of a potting compound(70), and the ends of the hollow fibres (21) being open; characterizedin that the end of the hollow fibre bundle (19) is cast by means of thepotting compound (70) substantially only within the support ring (40).2. Filter according to claim 1, characterized in that the support ring(40) comprises axially extending lugs (42).
 3. Filter according to claim1 or 2, characterized in that the axially extending lugs (42) arearranged on the side of the support ring (40) facing the centre of thehousing (3).
 4. Filter according to claim 1, characterized in that thehousing (3) comprises axially protruding lugs (42), upon which thesupport rings (40) are respectively seated.
 5. Filter according to anyprevious claim, characterized in that the lugs (42) are formed flexiblesuch that the support ring (40) is axially movable, to compensate foraxial shrinkages of the hollow-fibre bundle (19).
 6. Filter according toany previous claim, characterized in that the end-cap (5) is sealinglyjoined to the housing (3).
 7. Filter according to claim 6, characterizedin that the end-cap (5) is bonded or welded to the housing (3). 8.Filter according to claim 6, characterized in that the end-cap (5) issealingly joined to the housing (3) by means of a seal (60).
 9. Filteraccording to one of the previous claims, characterized in that itcomprises an inlet (7) and an outlet (9) for a first fluid, as well asat least one outlet (15) for a second fluid.
 10. Filter according toclaim 9, characterized in that the inlet (7) for the first fluid isarranged on one end-cap (5), and the outlet (9) for the first fluid isarranged on the other end-cap (5).
 11. Filter according to claim 10,characterized in that the outlet (15) for the second fluid is arrangedon an end-cap (5) or on the housing (3).
 12. Filter according to any ofclaims 9 to 11, characterized in that it comprises an inlet (13) for thesecond fluid.
 13. Filter according to claim 12, characterized in thatthe inlet (13) for the second fluid is arranged on an end-cap (5) or onthe housing (3).